Sinorhizobium meliloti low molecular mass phosphotyrosine phosphatase SMc02309 modifies activity of the UDP-glucose pyrophosphorylase ExoN involved in succinoglycan biosynthesis

Abstract

In Gram-negative bacteria, tyrosine phosphorylation has been shown to play a role in the control of exopolysaccharide (EPS) production. This study demonstrated that the chromosomal ORF SMc02309 from Sinorhizobium meliloti 2011 encodes a protein with significant sequence similarity to low molecular mass protein-tyrosine phosphatases (LMW-PTPs), such as the Escherichia coli Wzb. Unlike other well-characterized EPS biosynthesis gene clusters, which contain neighbouring LMW-PTPs and kinase, the S. meliloti succinoglycan (EPS I) gene cluster located on megaplasmid pSymB does not encode a phosphatase. Biochemical assays revealed that the SMc02309 protein hydrolyses p-nitrophenyl phosphate ( p-NPP) with kinetic parameters similar to other bacterial LMW-PTPs. Furthermore, we show evidence that SMc02309 is not the LMW-PTP of the bacterial tyrosine-kinase (BY-kinase) ExoP. Nevertheless, ExoN, a UDP-glucose pyrophosphorylase involved in the first stages of EPS I biosynthesis, is phosphorylated at tyrosine residues and constitutes an endogenous substrate of the SMc02309 protein. Additionally, we show that the UDP-glucose pyrophosphorylase activity is modulated by SMc02309-mediated tyrosine dephosphorylation. Moreover, a mutation in the SMc02309 gene decreases EPS I production and delays nodulation on Medicago sativa roots.

Characterization of Mutations That Affect the Nonoxidative Pentose Phosphate Pathway in Sinorhizobium meliloti

“…The latter modifications can occur in response to metabolite pools or environmental stimuli (45)(46)(47). In S. meliloti, the activity of ExoN, which is required for the synthesis of UDP-glucose, was shown to be modulated by its phosphorylation state (48). Taken together, these findings suggest that the changes in EPS I production in the mutant strains are likely due to changes in the hexose phosphate pools, resulting from a mutation in either transketolase or transaldolase.…”

Structural and Functional Properties, Biosynthesis, and Patenting Trends of Bacterial Succinoglycan: A Review

“…Three genes (exoC, exoB and exoN) are essential for sugar precursor synthesis, whereas exoY and exoF are for galactose addition to lipid carrier. exoN, a UDP-glucose pyrophosphorylase phosphorylate the tyrosine residue resulting into initial establishment of symbiosis [23]. Glycosyltransferases (GTs) encoded by exoALMOUW gene adds glucose residues and is also responsible for glycosidic bond formation.…”